In her article, Mrs May said her agreement with Brussels "puts Northern Ireland in a fantastic position for the future".

She also reassured unionists that "Northern Ireland's constitutional status as part of the United Kingdom is guaranteed".

Mrs May added: "Under this deal the future is certainly bright for Northern Ireland. It will be a gateway to both the EU market and the rest of the UK's market."

On the controversial backstop - the trading system that would operate on the island in the absence of a broader UK/EU deal - Mrs May said three things made it "an acceptable insurance policy".

She said the transition period could be extended instead of entering the backstop; regulations would be the same across all of the UK, and Northern Ireland would not be treated differently; and it would only be a temporary measure if used.

"And of course, in this situation, Northern Ireland would benefit from frictionless access to both the EU and the rest of the UK markets," she added.

But last night the rift between Mrs May and her DUP partners in the House of Commons widened. Eight DUP MPs sent a shot across Conservative bows by voting in support of a Labour amendment to the Finance Bill - reducing the Government's majority to just five. As well as voting with Labour on one amendment, DUP MPs also did not vote on three others.

The DUP is supposed to back the Government on Budget matters and on confidence votes.

While Sammy Wilson MP later insisted it did not mean the end of the DUP's deal with the Tories, he told BBC Radio 4's The World Tonight: "Since the Government has not honoured its side of the bargain we tonight tried to spell out some of the consequences of that being broken."

Earlier, Arlene Foster claimed the backstop is not needed to maintain a free flowing Irish border, as the Republic would never consider a hard border

The DUP leader was speaking after Taoiseach Leo Varadkar said he was "not contemplating" a hard border in the event of a no-deal Brexit. She said this represented evidence that it was "only ever a negotiating tactic by the European Union".

Although Mr Varadkar said on Sunday he was not contemplating a hard border in the event of a crash Brexit, on Friday he said one would be "very difficult to avoid" in a No Deal scenario.

Mrs Foster said: "We have been told that the backstop is only necessary to prevent such a hard border, but these comments make it clear that the EU's insistence on a backstop was not aimed at this. The European Union's focus on the border between Northern Ireland and the Republic has only ever been a negotiating tactic to secure its own aims in the negotiations.

"The Withdrawal Agreement was based on the false choice that an internal UK border was the only way to prevent a hard border between Northern Ireland and the Republic."

Meanwhile, David Trimble was part of a Brexiteer group who met Mrs May yesterday in a bid to get the deal renegotiated. The 'gang of four' - who are believed to have urged Mrs May to back a high-tech solution to keeping the Irish border open - were led by former party leader Iain Duncan Smith, and included Lord Lilley and MP Owen Paterson.

But moves by Tory Brexiteers to unseat Mrs May appear to have stalled. Last week they were confidently predicting they would get the 48 letters of no confidence needed to trigger a vote in her leadership.

But so far, there is no sign they have anything close to that, while the number who have publicly declared they submitted letters remains in the low 20s.

Earlier, Ulster Farmers' Union president Ivor Ferguson said leaving the EU without a deal has "consistently been found to be the worst of all possible options" by his organisation.

He said a No Deal Brexit would have "a devastating impact on farmers in Northern Ireland".

"While the Withdrawal Agreement is not perfect and we need clarification on some areas, the majority of farmers want to see the process move on," he said.

"Without a Withdrawal Agreement, this process can't even begin and on March 30 we crash out of the EU with no deal.